Method of and system for cooling a singulation process

ABSTRACT

A system for cooling at least one singulation saw used to singulate components from a substrate. The system is comprised of a coolant loop having at one or more coolant delivery means, a coolant collection means, one or more recycle tanks for contaminate particles to settle out of the captured coolant, a mixing tank configured after the recycle tanks within the loop to produce and replace lost coolant, and a means to cool the coolant. The system can all so include filters within the loop to remove particles not removed by the settling tank. Further, the system is able to be configured with a holding tank configured to prevent any bubbles from getting to the coolant delivery means.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of and incorporates by referenceprovisional application Ser. No. 60/901,547, filed Feb. 14, 2007, andentitled: CENTRALIZE COOLANT CLOSE LOOP.

FIELD OF THE INVENTION

The present invention relates generally to the field of substrateprocessing. More specifically, the invention relates to the cooling of asingulation saw blade used to singulate individual dies from asubstrate.

BACKGROUND OF THE INVENTION

Singulation is the process of cutting individual dies from their leadframes on a substrate containing a number of dies. When cutting asubstrate at a high speed, the resulting friction and resulting heatingof the substrate is an obstacle to high speed singulation. Excessiveheat from singulation can damage the die electronics and render the dieelectronics inoperative. Thus, coolant is used to cool and lubricate thecutting blade and substrate during singulation. FIG. 1 illustrates aprior art system 100 for cooling a saw blade 151 during singulation. Theprior art cooling system 100 includes a mixing system 110, a chemicaltank 120, a cooling coil 130, a pre-mixing filter 140, post mixingfilter 145 and a coolant delivery means 155. The mixing system 110 isfilled with deionized water from a deionized water source 125 and achemical from the chemical tank 120. The deionized water and thechemical are mixed in the mixing tank. This coolant within the mixingtank chamber 111 is chilled by the cooling coil 130. The fluid in themixing chamber 111 is pumped though a filter 145 and an coolant deliverymeans 155 delivers the coolant onto the saw blade 151 while singulatingthe dies from the substrate 152. The used coolant is captured by a pan157 for return to the mixing tank 110. This used coolant containssubstrate particles from the singulation process. The larger particlesare filtered out by a filter 140, such as a 100 micron filter. However,smaller particles enter the mixing system 110 and accumulate to form asludge in the bottom of the mixing tank chamber 111.

Eventually, the cooling system 100 and singulation saw 150 has to bestopped to clean the sludge from the mixing tank chamber 111 or to cleanor replace the filters 140 and 145. This stoppage causes a loss of thesingulation tool productivity and the removal of the sludge causes aloss of coolant. Further, the prior art system 100 is prone to theformation of bubbles which can travel into the cooling line from themixing and recirculation of the used coolant. These bubbles will causegaps in the delivery of coolant to the saw blade 151 which can causesudden heating of the sawblade 151 and thus potentially damage theelectronic components being singulated. A further disadvantage of theprior art system 100 is that the system is designed for a single sawwhich increases the space utilization for each singulation system.

What is needed is a cooling system that has less coolant loss, requiresless cleaning due to sludge buildup, does not introduce bubbles into thecoolant stream, and can provide coolant to more than one singulationsaw, and can continue to operate while cleaning the filters and tanks.

BRIEF SUMMARY OF THE INVENTION

The invention provides a structure for and method of providing a coolantflow in a singulation process.

It is to be understood that the terminology used herein is for thepurpose of describing particular aspects only and is not intended to belimiting. In this specification and in the claims which follow,reference will be made to a number of terms which shall be defined tohave the following meanings: it will be understood that, as used in thespecification and the appended claims, the singular forms “a,” “an,” and“the” include plural referents unless explicitely stated otherwise.“Optional” or “optionally” means that the subsequently described event,circumstance can or cannot occur, and that the description includesinstances where the event circumstance or construction can or cannotoccurs and instances where it does not. Ranges can be expressed hereinas from “about” one particular value, and/or to “about” anotherparticular value. When such a range is expressed, another aspectincludes from the one particular value and/or to the other particularvalue. Similarly, when values are expressed as approximations, by use ofthe antecedent “about,” it will be understood that the particular valueforms another aspect. Additional features and advantages of theinvention will be set forth in the description which follows, and inpart will be obvious from the description, or can be learned by thepractice of the invention. The features and advantages of the inventioncan be realized and obtained by means of the instruments andcombinations particularly pointed out in the appended claims. These andother features of the present invention will become more fully apparentfrom the following description and appended claims. Further, suchfeatures of the present invention can be learned by the practice of theinvention as set forth hereinafter.

A first aspect of the invention, is for a system for cooling at leastone singulation process. The system forms a first cooling loop thatincludes at least one coolant delivery means, a recycle coolantcollection means configured to capture a recycle coolant, at least onerecycle tanks configured for the settling of particulates from thecoolant, a mixing tank configure downstream of the recycle tank, and acoolant temperature control means.

In one embodiment, the singulation cooling system includes a bypass loopwhere some of the coolant within the first coolant loop bypasses thecoolant delivery means and passes back to the coolant temperaturecontrol means.

In a further embodiment, a plurality of course filters are placed in thecooling loop upstream of the mixing tank and configured to remove largeparticles from the coolant. In another embodiment, the cooling loopincludes a plurality of fine filters downstream of the mixing tank. Inone embodiment of the invention, multiple course filter elements areconfigured in a parallel format. In this way, at least one course filterelement can be removed and replaced or cleaned while the cooling systemis operating by closing the valves upstream and downstream of theremoved course filter element. multiple fine filter elements can beconfigured in a parallel format. Likewise, multiple fine filter elementscan be configures in a parallel format. Valves are installed upstreamand downstream of each fine filter element. In this way, at least onefine filter element can be removed and replace or cleaned while thecooling system is operating. It will be appreciated that this sequencecan be modified. For example, both course and fine filters can beupstream or downstream of the mixing tank. Preferably the course filteris upstream of the fine filter. In a further embodiment, the coursefilters are configured to remove particles 50-100 microns in size andthe fine filters are configured to remove particles between 10-25microns in size.

In a further embodiment, the singulation cooling loop includes a holdingtank where the holding tank is configured to prevent air bubbles fromgetting into the coolant delivery means. In a further embodiment, themixing tank includes of a controllable deionized water source inlet, acontrollable chemical inlet, a mixing tank coolant level detectionmeans, means for controlling the deionized water source inlet andchemical coolant inlet flow based on the coolant level, a recyclecoolant inlet, a coolant mixing means, and a mixing tank coolant outlet.In one embodiment, the temperature of the coolant is controlled to bebetween 18-20 degrees centigrade. In another embodiment, the holdingtank is configured for bubbles not to enter the coolant outlet and tohave a capacity of greater than 1000 liters.

In a second aspect of the invention, a method of generating a coolingloop for at least one singulation process is disclosed. The processsteps include controlling a coolant temperature, delivering the coolantto at least one singulation process and thereby generating a recyclecoolant, collecting the recycle coolant, settling particulates from therecycle coolant, and generating a mixed coolant by mixing the recyclecoolant, deionized water, and a chemical.

In one embodiment of the method further comprises the steps ofgenerating a coolant bypass loop wherein a bypass coolant flows inproximity to the one or more singulation processes, and generating acoolant by combining the mixed coolant and the bypass coolant.

In one embodiment, the recycle coolant is filtered. In a furtherembodiment, the coolant is also filtered. In an embodiment coursefiltering is performed before the mixing. In a further embodiment, thefiltering is performed by filtering elements that are replaceable whilethe cooling loop is operating. In one embodiment, the filtering isimplemented by filtering elements configured in parallel. In oneembodiment, the course filter is able to have filtering elements thatremove particulates ranging from 100-50 microns and the fine filterhaving filtering elements that remove particles from 10-25 microns.

In a further embodiment, the method of cooling at least one singulationprocesses includes removing air bubbles from the coolant and thereby thecoolant delivered to the singulation process is never substantiallyinterrupted by an air bubble. In one embodiment, the bubbles are removedin a tank that is greater than 1000 liters.

In another embodiment, the step of mixing the coolant includes the stepsof detecting the need for additional coolant, controlling the flow ofdeionized water for mixing, controlling the flow of a chemical formixing, and mixing the deionized water, chemical, and recycled coolant.In a further embodiment, the coolant temperature is controlled to bebetween 18-20 degrees centrigrade.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary illustration of a prior art singulation coolingsystem.

FIG. 2 is an exemplary illustration of one embodiment of a singulationprocess cooling system.

FIG. 3 is an exemplary illustration of the method step of a singulationcooling process.

In the drawings, like reference numbers are used when describing thesame elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention discloses a system for and a method of cooling asingulation process. Preferably, the singulation process uses a sawblade to cut electronic die components from a substrate. A singulationtool is a saw for cutting a substrate or a semiconductor wafer intoindividual electronic circuit dice.

FIG. 2 illustrates a system 200 for a cooling loop for the cooling of asingulation process. The system forms a coolant loop having of at leastone coolant deliver means 215, for delivering to saw blade 211. A usedcoolant collection apparatus 217 is coupled to deliver used coolant toone or more recycle tanks 220. A premixing filtering means 230, iscoupled to receive used coolant from the recycle tanks 220. A mixingsystem 240 is coupled to a received filtered used coolant from thepremixing filtering means 230 and also to a deionized water source 249and a chemical source 244. A post mixing filter 250, is coupled toreceive mixed coolant from the mixing system 240 and to deliver filteredcoolant to a holding tank 260. A heat exchange 270 receives coolant fromthe holding tank 260 and controls the temperature of the coolant to bewithin a predetermined range of temperatures . A bypass loop is formedby the coolant not used by the delivery means 215 and returned to theholding tank 160 through the bypass coolant return inlet 261.

The singulation process has comprised of one or more singulation saws210. Each saw 210 has a saw blade 211 for cutting a substrate 212 intosingle dice. Preferably the substrate 212 is a semiconductor substratebut other types of substrates are contemplated. The saw blade 211 andthe substrate 212 are cooled by a coolant provided by a delivery means215. The coolant delivery means 215 can be any standard means fordelivering a fluid under pressure, including but are not limited to apipe aperture, a nozzle, and a sprayer. The coolant absorbs cool heat toleast one of the saw blade 211 and the substrate 212.

A used coolant collection means 217 is provided for the capture andrecycling of the used coolant. The collection means preferably has a panlocated under the saw 210 but other collection means are contemplated.The saw 210 could be in an enclosed chamber from which the coolant iscollected, a vacuum system could be used for collection, or the floorwith a drain (not shown) near the singulation tool.

The recycle coolant collection means 217 is coupled to at least onerecycle tank 220. The recycle tank 220 is configured for thegravitational settling of any particulates from the recycle coolant.Preferably the recycle tanks 220 are in series but other configurationsare contemplated.

The particulates are particles of the substrate and of the sawbladegenerated when the saw 210 cuts the substrate 212. The one or morerecycle tanks 220 can be open or enclosed or a combination thereof.Further, the recycle tanks 220 can contain a means for removing theparticulate sludge that settles to the bottom of the tanks. The recycletanks 220 are able to be configured to be cleaned while the coolingsystem 200 is in operation or when not in operation.

An optional pre-mix filter 230 is coupled to receive used coolant fromthe recycle tanks 220 and to deliver coolant to the mixing tank 240. Thepremix filter 230 is shown in one embodiment having a first stage offiltering 232 and a second stage of filtering 234. The invention canembody a single stage of filtering or more than two stages of filtering.The first stage 232 and the second stage 234 are includes a plurality offilter elements 231 and 233 operating in parallel. These filter elements231 and 233 are configured to be replaceable while the cooling system isstill operating. Each filter element can have a valve coupled upstreamand another coupled downstream. By closing both valves the filterelement 3 operationably removed from the system. By closing both valvesthe filter element can be physically removed and replaced or cleaned. Inone embodiment, the pre-mix first stage 232 filter elements isconfigured to block larger particles than the second stage filterelements. In one embodiment, the first stage filters 232 are configuredto filter out 100 micron particles and the second stage filters 234 areconfigured to remove 50 micron particles.

The mixing system 240 is coupled to receive coolant from the pre-mixfilter 230. The mixing system 240 inputs recycled coolant into themixing tank 241 from the pre-mix filter inlet 247. When enough coolantis lost, either through evaporation, cleaning of the recycle tank 220,or through losses during singulation, replacement coolant is prepared inthe mixing tank 240. Preferably, the need for preparing more coolant isdetected by a tank level sensor 246. When an indication that additionalcoolant needs to be introduced deionized water (DI) is input into thetank chamber 241 from the DI inlet 243. A chemical is also added to themixing tank chamber 241 in a controlled ratio. The DI water, thechemical, and the recycled water are mixed by a mixer 242. The coolantresulting from the chemical mixed with the DI water preferably hasproperties in addition to including inhibiting oxidization andlubrication.

The mixing system outlet 248 is coupled to an optional post-mix filter250. The filter 250 is shown in one exemplary embodiment having a firststage of filtering 254 and a second stage of filtering 252. Alsocontemplated by the invention is an embodiment having a single stage offiltering or more than two stages of filtering. The first stage offiltering 254 and the second stage 254 preferably comprise a pluralityof filter elements 253 and 251 operating in parallel. These filterelements 251 and 252 are preferably able to be configured to bereplaceable while the cooling system 200 is still operating. In oneembodiment, the first stage 254 of filters are configured to filterlarger particles than the second stage. In one embodiment, the firststage filters 254 are configured to filter out substantially 25 micronor larger particles and the second stage filters 252 are configured toblock 10 micron or larger particles.

The holding tank 260 preferably is configured with a coolant inlet 262coupled to the post mixing filter 250, a coolant bypass inlet 261, andthe coolant delivery bypass inlet 261. The holding tank 260 is sized andconfigured to prevent bubbles from getting into the holding tank outlet263 and thereby interrupting the flow of cooling fluid to the saw blade211. In one embodiment, a tank size of 1000 liters provides sufficientvolume to prevent bubbles from being introduced into the cooling loop.The outlet of the holding tank is positioned to be below on upper levelof the coolant. The holding tank outlet 263 is coupled to the heatexchanger 270.

The heat exchanger 270 is configured to maintain a controlledtemperature of the coolant. The heat exchanger can be of a number oftypes including but not limited to shell and tube, plate heat exchanger,and a fluid heat exchanger. Preferably, the coolant is temperaturecontrolled to between 18-20 degrees centigrade.

It will be appreciated by one skilled in the art that a number of pumpsand valves can be placed within the circulation loops to control themovement of the coolant through the filters and into and out of tanksand to the coolant delivery means.

FIG. 3 shows an exemplary of the inventive steps for a method of 300 forthe cooling of a singulation process. The process is comprised ofcontrolling a coolant temperature 310, delivering the coolant to asingulation process 320, collection the recycle coolant 330, settlingthe particulates from the recycle coolant 350, generating a mixedcoolant 370, and removing air bubbles from the coolant 380.

The method begins but is not limited to beginning at step 310. At thestep 310, the coolant is temperature controlled. A temperature isselected that provides sufficient cooling during singulation but not socold as to cause thermal mechanical stresses to the substrate. Anyapplicable temperature control means can be used including including butnot limited to shell and tube, plate heat exchanger, and a fluid heatexchanger. Preferably, in this step the coolant is temperaturecontrolled to be a temperature between 18-20 degrees centigrade.

In a step 320, coolant is delivered to the singulation process. Thecoolant delivery means can be any method for delivering a coolant underpressure. These methods can include but are not limited to coolantflowing through a pipe aperture, a nozzle, or with a sprayer, preferablythrough a nozzle.

In a step 330, the coolant having been used for cooling is collected forrecycling. Any applicable collection method is contemplated includingbut not limited to gravitational flow, and vacuum. Preferably a pan isused to collect the recycle coolant.

In a step 340, the recycle coolant is put through a settling stepwherein particulates in the coolant are allowed to settle out of thecoolant. Preferably the settling occurs in one or more tanks where thebuild up of sludge can be cleaned from the tanks while the method ofcooling is on going.

In an optional step 350, the recycle coolant is filtered. Preferably therecycle coolant is filtered by a plurality of filtering elements whereina first stage the filtering remove 100 micron particles and in a secondstage the filtering elements removes 50 micron particles.

In a step 360, a mixed coolant is generated. Additional mixed coolant isformed when it is detected that there is a requirement for additionalcoolant. This indication can come from a coolant level indicator. Themixed coolant is generated by combining and mixing the recycle coolant,if available, and deionized water and a chemical in a controlled ratio.

In an optional step 370, the mixed coolant is filtered. Preferably thefiltering is performed in a manner such that the filtering componentscan be replenished, cleaned, or replaced while the singulation coolingmethod 300 is ongoing. Preferably the filtering of the mixed coolantremoves particles smaller than the particles removed in the optionalstep 350. Preferably the filtering is performed in two stages, thedownstream stage removing particles smaller than the stage upstream.Preferably the upstream filter stage removes particles substantially 25microns and more in size and the downstream filter stage removesparticles 10 microns and more in size.

In an optional step 280 air bubbles are removed from the coolant. Thebubbles are removed in a manner such that they are substantiallyeliminated from delivery to the singulation process. Preferably this isperformed by storing the coolant in a holding tank sufficiently largefor any bubble introduced by mixing or other means to settle out and bydrawing out coolant below a surface level of coolant in the holdingtank.

It will be readily apparent to those skilled in the art that the steps300 can be performed continuously, cyclically, and/or in batches. Also,it would be apparent to those skilled in the art that the steps withinthe inventive method 300 can be practiced in differing order and remainwithin the sprit of the invention.

In operation, the mixing tank 240 prepares enough coolant tosubstantially fill the holding tank 260. The deionized (DI) water inlet243 and chemical inlet 245 are configured to be input into the mixingtank chamber 241 DI water and chemical in a controlled ratio. Thecoolant is prepared with the mixer 242 and pumped to the holding tank260 through the post mixing filter 250 until the holding tank 260 issubstantially full. The DI inlet 243 and chemical inlet 245 areconfigured to stop the input when the mixing tank sensor 246 detects apredetermined tank level. The coolant is pumped to the heat exchanger270 to control the temperature of the coolant. Preferably, the coolantis cooled to 18-20 degrees centigrade. The coolant is then pumped to thecoolant delivery means 215 where a portion of the coolant is deliveredto the saw blade 211 and the cutting interface between the saw blade 211and the substrate 212. The remaining coolant returns to the holding tank260 through the coolant bypass inlet 261. Having a bypass loop has theadvantage of having coolant at the controlled temperature quicklyavailable at the coolant delivery means when it is time to start the saw210. Otherwise, the coolant can warm up in the line between the coolanttemperature control means and this warmed coolant would have to beflushed from the lines before starting singulation.

Reference has been made in detail to the preferred and alternativeembodiments of the invention, examples of which are illustrated in theaccompanying drawings. While the invention has been described inconjunction with the preferred embodiments, it will be understood thatthey are not intended to limit the invention to these embodiments. Onthe contrary, the invention is intended to cover alternatives,modifications and equivalents, which can be included within the spiritand scope of the invention. Furthermore, in the detailed description ofthe present invention, numerous specific details have been set forth inorder to provide a thorough understanding of the present invention.However, it should be noted that the present invention can be practicedwithout these specific details. In other instances, well known methods,procedures and components have not been described in detail as not tounnecessarily obscure aspects of the present invention.

1-10. (canceled)
 11. A method of generating a cooling loop for at leastone singulation process comprising the steps: a. controlling a coolanttemperature; b. delivering the coolant to one or more singulationprocesses thereby generating a recycle coolant; c. collecting therecycle coolant; d. settling particulates from the recycle coolant; ande. generating a mixed coolant by mixing the recycle coolant, deionizedwater, and a chemical.
 12. The method of claim 11, further comprisingthe step of filtering the recycle coolant.
 13. The method of claim 12,further comprising filtering the mixed coolant.
 14. The method of claim13, wherein the filtering the mixed coolant is comprising a plurality offine filter elements, wherein at least one fine filter elements isreplaceable while the cooling loop is operating.
 15. The method of claim14, wherein the filtering the recycle coolant comprises a plurality ofcourse filter elements, wherein at least one course filter element isexchangeable while the coolant loop is operating.
 16. The method ofclaim 15, wherein the course filter elements are configured in aparallel format and the fine filter elements are configured in aparallel format.
 17. The method of claim 16, wherein the course filterelements are configured to remove particles 50-100 microns in theirgreatest dimension and the fine filter elements are configured to removeparticles between 10-25 microns in their greatest dimension.
 18. Themethod of claim 12, further comprising the step of removing air bubblesfrom the coolant thereby delivering the coolant that is substantiallynever interrupted by an air bubble.
 19. The system of claim 18, whereinthe removing of the air bubbles is provided by a holding tank greaterthan 1000 liters.
 20. The method of claim 12, wherein the mixing of thecoolant is comprised of the steps: detecting a mixing tank coolantlevel; controlling the flow of deionized water into the mixing tankbased on the coolant level; controlling the flow of chemical into themixing tank based on the coolant level; and mixing the deionized water,chemical, and recycled coolant.
 21. The method of claim 11, whereincontrolling a coolant temperature comprises controlling the coolanttemperature to 18-20 degrees centigrade at the step of delivering thecoolant to one or more singulation processes thereby generating arecycle coolant.